Carbamoyl tetrazoles as inhibitors of endocannabinoid inactivation: A critical revisitation

Goods and Bads of the Endocannabinoid System as a Therapeutic Target: Lessons Learned after 30 Years

The cannabis derivative marijuana is the most widely used recreational drug in the Western world and is consumed by an estimated 83 million individuals (∼3% of the world population). In recent years, there has been a marked transformation in society regarding the risk perception of cannabis, driven by its legalization and medical use in many states in the United States and worldwide. Compelling research evidence and the Food and Drug Administration cannabis-derived cannabidiol approval for severe childhood epilepsy have confirmed the large therapeutic potential of cannabidiol itself, Δ9-tetrahydrocannabinol and other plant-derived cannabinoids (phytocannabinoids). Of note, our body has a complex endocannabinoid system (ECS)-made of receptors, metabolic enzymes, and transporters-that is also regulated by phytocannabinoids. The first endocannabinoid to be discovered 30 years ago was anandamide (N-arachidonoyl-ethanolamine); since then, distinct elements of the ECS have been the target of drug design programs aimed at curing (or at least slowing down) a number of human diseases, both in the central nervous system and at the periphery. Here a critical review of our knowledge of the goods and bads of the ECS as a therapeutic target is presented to define the benefits of ECS-active phytocannabinoids and ECS-oriented synthetic drugs for human health. SIGNIFICANCE STATEMENT: The endocannabinoid system plays important roles virtually everywhere in our body and is either involved in mediating key processes of central and peripheral diseases or represents a therapeutic target for treatment. Therefore, understanding the structure, function, and pharmacology of the components of this complex system, and in particular of key receptors (like cannabinoid receptors 1 and 2) and metabolic enzymes (like fatty acid amide hydrolase and monoacylglycerol lipase), will advance our understanding of endocannabinoid signaling and activity at molecular, cellular, and system levels, providing new opportunities to treat patients.

Efficient synthesis of tetrazole hemiaminal silyl ethers via three-component hemiaminal silylation

An efficient route to construct 2,5-disubstituted tetrazole hemiaminal silyl ethers via one-pot three-component hemiaminal silylation of 5-substituted tetrazoles, aldehydes, and silyl triflates was developed. Diverse 2,5-disubstituted tetrazole hemiaminal silyl ethers were obtained with 37 : 63->99 : 1 regioisomeric ratios. The regioselectivities of this reaction were significantly affected by steric hindrance and the conjugation effects of substitutions on the 5-position of tetrazoles.

1-Heteroarylpropan-2-ones as inhibitors of fatty acid amide hydrolase: Studies on structure-activity relationships and metabolic stability

The serine hydrolase fatty acid amide hydrolase (FAAH) catalyzes the degradation of the endocannabinoid anandamide, which possesses analgesic and anti-inflammatory effects. A new series of 1-heteroarylpropan-2-ones was synthesized and evaluated for FAAH inhibition. Structure-activity relationship studies revealed that 1H-benzotriazol-1-yl, 1H-7-azabenzotriazol-1-yl, 1H-tetrazol-1-yl and 2H-tetrazol-2-yl substituents have the highest impact on inhibitory potency. Furthermore, attempts were made to increase the limited metabolic stability of the ketone functionality of these compounds towards metabolic reduction by introduction of shielding alkyl substituents in proximity of this serine reactive group.

Hit to lead optimization of a series of N-[4-(1,3-benzothiazol-2-yl)phenyl]acetamides as monoacylglycerol lipase inhibitors with potential anticancer activity

A total of thirty five new N-[4-(1,3-benzothiazol-2-yl)phenyl]acetamide derivatives were synthesized and structures of all the compounds were confirmed on the basis of elemental analysis and collective use of IR, (1)H NMR, (13)C NMR and mass spectral data. Compounds were tested for their ability to inhibit human monoacylglycerol lipase (hMAGL) enzyme. Eight compounds 4, 19-21, 24-26, and 34 reduced the hMAGL activity less than 50% at 100 nM concentrations. The halogen substituted aniline derivatives 20, 21 and 24-26 were found to be most active among all the synthesized compounds having IC50 value in the range of 6.5-9 nM. Twenty five compounds were selected by NCI, USA for one dose anticancer screening. Compound 21 (NSC: 780167) and 24 (NSC: 780168) fulfilled prearranged doorstep growth inhibition criteria and further selected for NCI full panel five dose assay at 10-fold dilutions of five different concentrations (0.01, 0.1, 1, 10 and 100 μM). Both the compounds 21 and 24 were found to be most active against MCF7 and MDA-MB-468 breast cancer cell lines. The GI50 value of 32.5 nM (MCF7) and 23.8 nM (MDA-MB-468) was observed for compound 21. Compound 24 showed GI50 values of 37.1 nM against MCF7 breast cancer cell line and 25.1 nM against MDA-MB-468 breast cancer cell line.

Structure Property Relationships of Carboxylic Acid Isosteres

The replacement of a carboxylic acid with a surrogate structure, or (bio)-isostere, is a classical strategy in medicinal chemistry. The general underlying principle is that by maintaining the features of the carboxylic acid critical for biological activity, but appropriately modifying the physicochemical properties, improved analogs may result. In this context, a systematic assessment of the physicochemical properties of carboxylic acid isosteres would be desirable to enable more informed decisions of potential replacements to be used for analog design. Herein we report the structure–property relationships (SPR) of 35 phenylpropionic acid derivatives, in which the carboxylic acid moiety is replaced with a series of known isosteres. The data set generated provides an assessment of the relative impact on the physicochemical properties that these replacements may have compared to the carboxylic acid analog. As such, this study presents a framework for how to rationally apply isosteric replacements of the carboxylic acid functional group.

Endocannabinoid transport revisited

Endocannabinoids are arachidonic acid-derived endogenous lipids that activate the endocannabinoid system which plays a major role in health and disease. The primary endocannabinoids are anandamide (AEA, N-arachidonoylethanolamine) and 2-arachidonoyl glycerol. While their biosynthesis and metabolism have been studied in detail, it remains unclear how endocannabinoids are transported across the cell membrane. In this review, we critically discuss the different models of endocannabinoid trafficking, focusing on AEA cellular uptake which is best studied. The evolution of the current knowledge obtained with different AEA transport inhibitors is reviewed and the confusions caused by the lack of their specificity discussed. A comparative summary of the most important AEA uptake inhibitors and the studies involving their use is provided. Based on a comprehensive literature analysis, we propose a model of facilitated AEA membrane transport followed by intracellular shuttling and sequestration. We conclude that novel and more specific probes will be essential to identify the missing targets involved in endocannabinoid membrane transport.

Design, synthesis, in vitro antimicrobial and cytotoxic evaluation of novel 1,2,3-selena/thiadiazolyltetrazole derivatives

A new series of 2,5-disubstituted tetrazoles and 1,2,3-selena/thiadiazolyl-2H-tetrazole derivatives were synthesized and evaluated for theirin vitroantimicrobial and cytotoxic activities against pathogenic strains.

Tetrazole regioisomers in the development of nitro group-containing antitubercular agents

Tetrazole derivatives containing nitro substituents have been identified as promising antitubercular agents.

Inhibitors of Fatty Acid Amide Hydrolase and Monoacylglycerol Lipase: New Targets for Future Antidepressants

Cannabis and analogs of Δ⁹-tetrahydrocannabinol have been used for therapeutic purposes, but their therapeutic use remains limited because of various adverse effects. Endogenous cannabinoids have been discovered, and dysregulation of endocannabinoid signaling is implicated in the pathophysiology of major depressive disorder (MDD). Recently, endocannabinoid hydrolytic enzymes such as fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have become new therapeutic targets in the treatment of MDD. Several FAAH or MAGL inhibitors are reported to have no cannabimimetic side effects and, therefore, are new potential therapeutic options for patients with MDD who are resistant to first-line antidepressants (selective serotonin and serotonin-norepinephrine reuptake inhibitors). In this review, we focus on the possible relationships between MDD and the endocannabinoid system as well as the inhibitors' therapeutic potential. MAGL inhibitors may reduce inflammatory responses through activation of cannabinoid receptor type 2. In the hypothalamic-pituitary-adrenal axis, repeated FAAH inhibitor administration may be beneficial for reducing circulating glucocorticoid levels. Both FAAH and MAGL inhibitors may contribute to dopaminergic system regulation. Recently, several new inhibitors have been developed with strong potency and selectivity. FAAH inhibitor, MAGL inhibitor, or dual blocker use would be promising new treatments for MDD. Further pre-clinical studies and clinical trials using these inhibitors are warranted.

A review of syntheses of 1,5-disubstituted tetrazole derivatives

This report provides a brief overview of the various representative literature procedures for the synthesis of 1,5-disubstituted tetrazoles (1,5-DSTs) and fused 1,5-disubstituted tetrazoles with more than 120 references. Most of the published methods for the synthesis of 1,5-DSTs include the use of nitriles, amides, thioamides, imidoyl chlorides, heterocumulenes, isocyanates, isothiocyanates, carbodiimides, ketenimines, ketones, amines, and alkenes as the starting materials. The transformation of 1- and 5-substituted tetrazoles into 1,5-DSTs is also covered in this report.

Docking based virtual screening and molecular dynamics study to identify potential monoacylglycerol lipase inhibitors

Monoacylglycerol lipase (MAGL) is one of the key enzymes of the endocannabinoid system (ECS). It hydrolyzes one of the major endocannabinoid, 2-arachidonoylglycerol (2-AG), an endogenous full agonist at G protein coupled cannabinoid receptors CB1 and CB2. Numerous studies showed that MGL inhibitors are potentially useful for the treatment of pain, inflammation, cancer and CNS disorders. These provocative findings suggested that pharmacological inhibition of MAGL function may confer significant therapeutic benefits. In this study, we presented hybrid ligand and structure-based approaches to obtain a novel set of virtual leads as MAGL inhibitors. The constraints used in this study, were Glide score, binding free energy estimates and ADME properties to screen the ZINC database, containing approximately 21 million compounds. A total of seven virtual hits were obtained, which showed significant binding affinity towards MAGL protein. Ligand, ZINC24092691 was employed in complex form with the protein MAGL, for molecular dynamics simulation study, because of its excellent glide score, binding free energy and ADME properties. The RMSD of ZINC24092691 was observed to stay at 0.1 nm (1 Å) in most of the trajectories, which further confirmed its ability to inhibit the protein MAGL. The hits were then evaluated for their ability to inhibit human MAGL. The compound ZINC24092691 displayed the noteworthy inhibitory activity reducing MAGL activity to 21.15% at 100 nM concentration, with an IC50 value of 10 nM.

Characterization of four new designer drugs, 5-chloro-NNEI, NNEI indazole analog, α-PHPP and α-POP, with 11 newly distributed designer drugs in illegal products

Our continuous survey of illegal products in Japan revealed the new distribution of 15 designer drugs. We identified four synthetic cannabinoids, i.e., NNEI (1), 5-fluoro-NNEI (2), 5-chloro-NNEI (3) and NNEI indazole analog (4), and seven cathinone derivatives, i.e., MPHP (5), α-PHPP (6), α-POP (7), 3,4-dimethoxy-α-PVP (8), 4-fluoro-α-PVP (9), α-ethylaminopentiophenone (10) and N-ethyl-4-methylpentedrone (11). We also determined LY-2183240 (12) and its 2'-isomer (13), which were reported to inhibit endocannabinoid uptake, a methylphenidate analog, 3,4-dichloromethylphenidate (14), and an MDA analog, 5-APDB (15). No chemical and pharmaceutical data for compounds 3, 4, 6 and 7 had been reported, making this the first report on these compounds.

Chemical probes of endocannabinoid metabolism

The endocannabinoid signaling system regulates diverse physiologic processes and has attracted considerable attention as a potential pharmaceutical target for treating diseases, such as pain, anxiety/depression, and metabolic disorders. The principal ligands of the endocannabinoid system are the lipid transmitters N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), which activate the two major cannabinoid receptors, CB1 and CB2. Anandamide and 2-AG signaling pathways in the nervous system are terminated by enzymatic hydrolysis mediated primarily by the serine hydrolases fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. In this review, we will discuss the development of FAAH and MAGL inhibitors and their pharmacological application to investigate the function of anandamide and 2-AG signaling pathways in preclinical models of neurobehavioral processes, such as pain, anxiety, and addiction. We will place emphasis on how these studies are beginning to discern the different roles played by anandamide and 2-AG in the nervous system and the resulting implications for advancing endocannabinoid hydrolase inhibitors as next-generation therapeutics.

Equipotent inhibition of fatty acid amide hydrolase and monoacylglycerol lipase - dual targets of the endocannabinoid system to protect against seizure pathology

Advances in the understanding of the endogenous cannabinoid system have led to several therapeutic indications for new classes of compounds that enhance cannabinergic responses. Endocannabinoid levels are elevated during pathogenic conditions, and inhibitors of endocannabinoid inactivation promote such on-demand responses. The endocannabinoids anandamide and 2-arachidonoyl glycerol have been implicated in protective signaling against excitotoxic episodes, including seizures. To better understand modulatory pathways that can exploit such responses, we used the new generation compound AM6701 that blocks both the anandamide-deactivating enzyme fatty acid amide hydrolase (FAAH) and the 2-arachidonoyl glycerol-deactivating enzyme monoacylglycerol lipase (MAGL) with equal potency. Also studied was the structural isomer AM6702 which is 44-fold more potent for inhibiting FAAH versus MAGL. When applied before and during kainic acid (KA) exposure to cultured hippocampal slices, AM6701 protected against the resulting excitotoxic events of calpain-mediated cytoskeletal damage, loss of presynaptic and postsynaptic proteins, and pyknotic changes in neurons. The equipotent inhibitor was more effective than its close relative AM6702 at protecting against the neurodegenerative cascade assessed in the slice model. In vivo, AM6701 was also the more effective compound for reducing the severity of KA-induced seizures and protecting against behavioral deficits linked to seizure damage. Corresponding with the behavioral improvements, cytoskeletal and synaptic protection was elicited by AM6701, as found in the KA-treated hippocampal slice model. It is proposed that the influence of AM6701 on FAAH and MAGL exerts a synergistic action on the endocannabinoid system, thereby promoting the protective nature of cannabinergic signaling to offset excitotoxic brain injury.

Development and characterization of endocannabinoid hydrolases FAAH and MAGL inhibitors bearing a benzotriazol-1-yl carboxamide scaffold

A series of (1H-benzo[d][1,2,3]triazol-1-yl)(4-benzylpiperazin-1-yl)methanones and of (1H-benzo[d][1,2,3]triazol-1-yl)(4-phenylpiperazin-1-yl)methanones has been prepared and tested on human fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL). In the benzylpiperazinyl series, compound 29 (ML30) exhibited an IC(50) value of 0.54 nM on MAGL, combined with a 1000-fold selectivity versus FAAH, while compounds 11 and 16 acted as potent dual FAAH-MAGL inhibitors (IC(50)<10 nM). In the phenylpiperazinyl series, compounds 37, 38, 42, and 43 displayed IC(50) values against MAGL in the nanomolar range, whilst being between one and two orders of magnitude less potent on the FAAH, while compounds 31 and 32 were potent FAAH inhibitors (IC(50)<20 nM) and over 12-fold selective versus MAGL. The key structural determinants driving the structure-activity relationships were explored by the minimization of the inhibitors inside the active site of both enzymes.

Assay and inhibition of diacylglycerol lipase activity

A series of N-formyl-α-amino acid esters of β-lactone derivatives structurally related to tetrahydrolipstatin (THL) and O-3841 were synthesized that inhibit human and murine diacylglycerol lipase (DAGL) activities. New ether lipid reporter compounds were developed for an in vitro assay to efficiently screen inhibitors of 1,2-diacyl-sn-glycerol hydrolysis and related lipase activities using fluorescence resonance energy transfer (FRET). A standardized thin layer chromatography (TLC) radioassay of diacylglycerol lipase activity utilizing the labeled endogenous substrate [1″-(14)C]1-stearoyl-2-arachidonoyl-sn-glycerol with phosphorimaging detection was used to quantify inhibition by following formation of the initial product [1″-(14)C]2-arachidonoylglycerol and further hydrolysis under the assay conditions to [1-(14)C]arachidonic acid.

The design, synthesis and biological evaluation of novel URB602 analogues as potential monoacylglycerol lipase inhibitors

We have synthesised an extensive series of URB602 analogues as inhibitors of monoacylglycerol lipase (MAGL), which is the major enzyme responsible for metabolising the endocannabinoid 2-arachidonylglycerol. The recently identified crystal structure of MAGL was used in the design strategy and revealed three possible binding sites for URB602 and the proposed analogues. A test series of carbamate analogues were docked into the identified sites to predict the most favourable binding location. The synthesised analogues of URB602 explored the biological effects of isosteric replacement, ring size and substitution, para substitution of the biphenyl moiety and the incorporation of a bicyclic element. The compounds were tested for their ability to inhibit human MAGL. The carbamate analogue 16 displayed the most significant inhibitory activity, reducing MAGL activity to 26% of controls at 100 μM compared to 73% for the parent compound URB602.

Inactivation of Anandamide Signaling: A Continuing Debate

Since the first endocannabinoid anandamide was identified in 1992, extensive research has been conducted to characterize the elements of the tightly controlled endocannabinoid signaling system. While it was established that the activity of endocannabinoids are terminated by a two-step process that includes cellular uptake and degradation, there is still a continuing debate about the mechanistic role of these processes in inactivating anandamide signals.

Identification by nuclear magnetic resonance spectroscopy of an active-site hydrogen-bond network in human monoacylglycerol lipase (hMGL): implications for hMGL dynamics, pharmacological inhibition, and catalytic mechanism

Intramolecular hydrogen bonding is an important determinant of enzyme structure, catalysis, and inhibitor action. Monoacylglycerol lipase (MGL) modulates cannabinergic signaling as the main enzyme responsible for deactivating 2-arachidonoylglycerol (2-AG), a primary endocannabinoid lipid messenger. By enhancing tissue-protective 2-AG tone, targeted MGL inhibitors hold therapeutic promise for managing pain and treating inflammatory and neurodegenerative diseases. We report study of purified, solubilized human MGL (hMGL) to explore the details of hMGL catalysis by using two known covalent hMGL inhibitors, the carbamoyl tetrazole AM6701 and N-arachidonoylmaleimide (NAM), that act through distinct mechanisms. Using proton nuclear magnetic resonance spectroscopy (NMR) with purified wild-type and mutant hMGLs, we have directly observed a strong hydrogen-bond network involving Asp239 and His269 of the catalytic triad and neighboring Leu241 and Cys242 residues. hMGL inhibition by AM6701 alters this hydrogen-bonding pattern through subtle active-site structural rearrangements without influencing hydrogen-bond occupancies. Rapid carbamoylation of hMGL Ser122 by AM6701 and elimination of the leaving group is followed by a slow hydrolysis of the carbamate group, ultimately regenerating catalytically competent hMGL. In contrast, hMGL titration with NAM, which leads to cysteine alkylation, stoichiometrically decreases the population of the active-site hydrogen bonds. NAM prevents reformation of this network, and in this manner inhibits hMGL irreversibly. These data provide detailed molecular insight into the distinctive mechanisms of two covalent hMGL inhibitors and implicate a hydrogen-bond network as a structural feature of hMGL catalytic function.

Crystal structure of the human monoacylglycerol lipase, a key actor in endocannabinoid signaling

2-Arachidonoylglycerol plays a major role in endocannabinoid signaling, and is tightly regulated by the monoacylglycerol lipase (MAGL). Here we report the crystal structure of human MAGL. The protein crystallizes as a dimer, and despite structural homologies to haloperoxidases and esterases, it distinguishes itself by a wide and hydrophobic access to the catalytic site. An apolar helix covering the active site also gives structural insight into the amphitropic character of MAGL, and likely explains how MAGL interacts with membranes to recruit its substrate. Docking of 2-arachidonoylglycerol highlights a hydrophobic and a hydrophilic cavity that accommodate the lipid into the catalytic site. Moreover, we identified Cys201 as the crucial residue in MAGL inhibition by N-arachidonylmaleimide, a sulfhydryl-reactive compound. Beside the advance in the knowledge of endocannabinoids degradation routes, the structure of MAGL paves the way for future medicinal chemistry works aimed at the design of new drugs exploiting 2-arachidonoylglycerol transmission.

Refined homology model of monoacylglycerol lipase: toward a selective inhibitor

Monoacylglycerol lipase (MGL) is primarily responsible for the hydrolysis of 2-arachidonoylglycerol (2-AG), an endocannabinoid with full agonist activity at both cannabinoid receptors. Increased tissue 2-AG levels consequent to MGL inhibition are considered therapeutic against pain, inflammation, and neurodegenerative disorders. However, the lack of MGL structural information has hindered the development of MGL-selective inhibitors. Here, we detail a fully refined homology model of MGL which preferentially identifies MGL inhibitors over druglike noninhibitors. We include for the first time insight into the active-site geometry and potential hydrogen-bonding interactions along with molecular dynamics simulations describing the opening and closing of the MGL helical-domain lid. Docked poses of both the natural substrate and known inhibitors are detailed. A comparison of the MGL active-site to that of the other principal endocannabinoid metabolizing enzyme, fatty acid amide hydrolase, demonstrates key differences which provide crucial insight toward the design of selective MGL inhibitors as potential drugs.

Pain and beyond: fatty acid amides and fatty acid amide hydrolase inhibitors in cardiovascular and metabolic diseases

Fatty acid amide hydrolase (FAAH) is responsible for the hydrolysis of several important endogenous fatty acid amides (FAAs), including anandamide, oleoylethanolamide and palmitoylethanolamide. Because specific FAAs interact with cannabinoid and vanilloid receptors, they are often referred to as 'endocannabinoids' or 'endovanilloids'. Initial interest in this area, therefore, has focused on developing FAAH inhibitors to augment the actions of FAAs and reduce pain. However, recent literature has shown that these FAAs - through interactions with unique receptors (extracellular and intracellular) - can induce a diverse array of effects that include appetite suppression, modulation of lipid and glucose metabolism, vasodilation, cardiac function and inflammation. This review gives an overview of FAAs and diverse FAAH inhibitors and their potential therapeutic utility in pain and non-pain indications.

Azole antimicrobial pharmacophore-based tetrazoles: synthesis and biological evaluation as potential antimicrobial and anticonvulsant agents

The azole pharmacophore is still considered a viable lead structure for the synthesis of more efficacious and broad spectrum antimicrobial agents. Potential antibacterial and antifungal activities are encountered with some tetrazoles. Therefore, this study presents the synthesis and antimicrobial evaluation of a new series of substituted tetrazoles that are structurally related to the famous antimicrobial azole pharmacophore. A detailed discussion of the structural elucidation of some of the newly synthesized compounds is also described. Antimicrobial evaluation revealed that twenty compounds were able to display variable growth inhibitory effects on the tested Gram positive and Gram negative bacteria with special efficacy against the Gram positive strains. Meanwhile, six compounds exhibited moderate antifungal activity against Candida albicans and Aspergillus fumigatus. Structurally, the antibacterial activity was encountered with tetrazoles containing a phenyl substituent, while the obtained antifungal activity was confined to the benzyl variants. Compounds 16, 18, 24 and 27 were proved to be the most active antibacterial members within this study with a considerable broad spectrum against all the Gram positive and negative strains tested. A distinctive anti-Gram positive activity was displayed by compound 18 against Staphylococcus aureus that was equipotent to ampicillin (MIC 6.25 microg/mL). On the other hand, twelve compounds were selected to be screened for their preliminary anticonvulsant activity against subcutaneous metrazole (ScMet) and maximal electroshock (MES) induced seizures in mice. The results revealed that five compounds namely; 3, 5, 13, 21, and 24 were able to display noticeable anticonvulsant activity in both tests at 100 mg/kg dose level. Compounds 5 and 21 were proved to be the most active anticonvulsant members in this study with special high activity in the ScMet assay (% protection: 100% and 80%, respectively).

Covalent inhibitors of human monoacylglycerol lipase: ligand-assisted characterization of the catalytic site by mass spectrometry and mutational analysis

The active site of recombinant hexa-histidine-tagged human monoacylglycerol lipase (hMGL) is characterized by mass spectrometry using the inhibitors 5-((biphenyl-4-yl)methyl)-N,N-dimethyl-2H-tetrazole-2-carboxamide (AM6701), and N-arachidonylmaleimide (NAM) as probes. Carbamylation of Ser(129) by AM6701 in the putative hMGL catalytic triad demonstrates this residue's essential role in catalysis. Partial NAM alkylation of hMGL cysteine residues 215 and/or 249 was sufficient to achieve approximately 80% enzyme inhibition. Although Cys(215) and/or Cys(249) mutations to alanine(s) did not affect hMGL hydrolytic activity as compared with nonmutated hMGL, the C215A displayed heightened NAM sensitivity, whereas the C249A evidenced reduced NAM sensitivity. These data conclusively demonstrate a sulfhydryl-based mechanism for NAM inhibition of hMGL in which Cys(249) is of paramount importance. Identification of amino acids critical to the catalytic activity and pharmacological modulation of hMGL informs the design of selective MGL inhibitors as potential drugs.

Membrane microdomains and metabolic pathways that define anandamide and 2-arachidonyl glycerol biosynthesis and breakdown

Anandamide (AEA) and 2-arachidonyl glycerol (2-AG), endogenous ligands for the CB1 and CB2 cannabinoid receptors, are referred to as endocannabinoids because they mimic the actions of delta9-tetrahydrocannabinol (Delta9-THC), a plant-derived cannabinoid. The processes by which AEA and 2-AG are biosynthesized, released, taken up by cells and hydrolyzed have been of much interest as potential therapeutic targets. In this review we will discuss the progress that has been made to characterize the primary pathways for AEA and 2-AG formation and breakdown as well as the role that specialized membrane microdomains known as lipid rafts play in these processes. Furthermore we will review the recent advances made to track and detect AEA in biological matrices.

Antinociceptive effects of tetrazole inhibitors of endocannabinoid inactivation: cannabinoid and non-cannabinoid receptor-mediated mechanisms

BACKGROUND AND PURPOSE

Tetrazoles were recently developed as inhibitors of the cellular uptake of the endocannabinoid anandamide or of its hydrolysis by fatty acid amide hydrolase (FAAH), but were proposed to act also on non-endocannabinoid-related serine hydrolases.

EXPERIMENTAL APPROACH

We tested, in a model of inflammatory pain induced in mice by formalin, five chemically similar inhibitors: (i) OMDM119 and OMDM122, two potent carbamoyl tetrazole FAAH inhibitors with no effect on anandamide uptake; (ii) LY2183240, a carbamoyl tetrazole with activity as both FAAH and uptake inhibitor; (iii) OMDM132, a non-carbamoyl tetrazole with activity only as uptake inhibitor and iv) OMDM133, a non-carbamoyl tetrazole with no activity at either FAAH or uptake.

RESULTS

All compounds (2.5-10 mg kg(-1), i.p.) inhibited the second phase of the nocifensive response induced by intraplantar injection of formalin. The effects of OMDM119, OMDM122 and OMDM133 were not antagonized by pretreatment with cannabinoid CB(1) receptor antagonists, such as rimonabant or AM251 (1-3 mg kg(-1), i.p.). The effects of LY2183240 and OMDM132 were fully or partially antagonized by rimonabant, respectively, and the latter compound was also partly antagonized by the CB(2) receptor antagonist, AM630.

CONCLUSIONS AND IMPLICATIONS

(i) non-FAAH hydrolases might be entirely responsible for the antinociceptive activity of some, but not all, tetrazole FAAH inhibitors, (ii) the presence of a carbamoylating group is neither necessary nor sufficient for such compounds to act through targets other than FAAH and (iii) inhibition of anandamide uptake is responsible for part of this antinociceptive activity, independently of effects on FAAH.

Targeting the endocannabinoid system: to enhance or reduce?

As our understanding of the endocannabinoids improves, so does the awareness of their complexity. During pathological states, the levels of these mediators in tissues change, and their effects vary from those of protective endogenous compounds to those of dysregulated signals. These observations led to the discovery of compounds that either prolong the lifespan of endocannabinoids or tone down their action for the potential future treatment of pain, affective and neurodegenerative disorders, gastrointestinal inflammation, obesity and metabolic dysfunctions, cardiovascular conditions and liver diseases. When moving to the clinic, however, the pleiotropic nature of endocannabinoid functions will require careful judgement in the choice of patients and stage of the disorder for treatment.

Aqueous humor outflow effects of 2-arachidonylglycerol

This study was conducted to test the effects of 2-arachidonylglycerol (2-AG), an endocannabinoid, on aqueous humor outflow facility, to study the cellular mechanisms of 2-AG, and to investigate the possible existence and activity of monoacylgylcerol lipase (MGL), a 2-AG metabolic enzyme, in the trabecular meshwork (TM). The effects of 2-AG on aqueous humor outflow facility were measured using an anterior segment perfused organ culture model. The expression and activity of MGL in TM tissues were assessed using Western blot analysis and an enzyme activity assay respectively. 2-AG induced activation of p42/44 mitogen-activated protein (MAP) kinase was determined by Western blot analysis using an anti-phospho p42/44 MAP kinase antibody. AlexaFluor 488-labeled phalloidin staining was used to examine actin filament in cultured TM cells. Administration of 10nM of 2-AG caused a transient enhancement of aqueous humor outflow. In the presence of 100nM of LY2183240, an inhibitor of MGL, the effect of 10nM of 2-AG on outflow was prolonged by at least 4h. The 2-AG-induced enhancement of outflow was blocked by SR141716A, a CB1 antagonist, and SR144528, a CB2 antagonist. In Western blot studies, a 35kDa band representing MGL was detected on TM tissues with an anti-MGL antibody. The 2-AG enzymatic hydrolysis activity was detected in TM tissues and this activity was reduced by 70.1+/-5.3% with the addition of 100 nM of LY2183240. Treatment of trabecular meshwork cells with 10nM of 2-AG plus 100 nM LY2183240 for 5h evoked phosphorylation of p42/44 MAP kinase. The 2-AG-induced enhancement of p42/44 MAP kinase phosphorylation was blocked by pretreatment with SR141716A, SR144528, as well as PD98059, an inhibitor of the p42/44 MAP kinase pathway. In addition, the outflow-enhancing effect of 2-AG was blocked by pretreatment with PD98059. Furthermore, treatment with 2-AG plus LY2183240 caused rounding of TM cells and a reduction of actin stress fibers in TM cells. Pretreatment with SR141716A, SR144528, and PD98059 blocked these 2-AG-induced morphology and cytoskeleton changes in TM cells. In conclusion, the results from this study demonstrate that administration of 2-AG increases aqueous humor outflow facility and this effect of 2-AG is mediated through both the CB1 and CB2 cannabinoid receptors. In addition, this study reveals the existence and the activity of MGL, a 2-AG metabolizing enzyme, in the TM tissues. Furthermore, this study suggests that 2-AG-induced enhancement of outflow facility involves the p42/44 MAP kinase signaling pathway and changes in actin cytoskeletons in TM cells.